Spark plug electrode



June 6, 1944. J. R JG'RETZINGR ETAL 2,350,396

{ PARK PLUG ELECT umanam- E.:

n 226307/ @n sz% MW l(lttcarnegs Patented June 6, 1944 sraax PLUGELEcraonE John B.. Gretzlnger, Alexander J. Battey, and Hector Rabenana.Flint, Mich., assignors to General Motors Corporation. Detroit, Mich., acorporation of Delaware Application September 22, 1941, Serial No.411,814

6 Claims.

This invention relates to spark plugs, particularly to spark plugelectrodes.

With many types of plugs made today some difllcultyhas been experiencedwith the sparking end of the insulator. Because of the diillculty ofobtaining a cement having a satisfactory coeillcient of expansion, ithas been found expedient to mount the electrode in the insulator so thatit is spaced from .the insulator by an air gap through a substantialpart of the sparking end of its length. To increase the dielectric pathbetween the conductor shell and the insulator, it is desirable toprovide clearance space between the sparking end of the insulator andthe shell, leaving that end of the insulator unsupported. It has furtherbeen found advantageous to make electrodes which`are separate from thespark plug terminal, and to seal the electrode in the insulator by meansof a material which'bonds itself to both the electrodev and theinsulator to form a substantially gas tight joint. This sealing materialis electrically conductive to complete the circuit between the terminaland the electrode. It has been found, however, that with plugs of this,type, shocks or jars transmitted to the plug tend to cause vibration ofthe electrode in the course of which the free or sparking end of theelectrode may strike the thin, unsupported tip of the insulator,resulting in chipping of said tip.

Figure 3 is a section on line 3-3 of Figure 2.

Figures 4-10 illustrate alternative methods of practising thisinvention.

Figure 1 shows a spark plug having a conductor shell 2. An insulator 4of any suitable material is secured in conductor shell 2 between gaskets6 and 8. The lower portion III of insulator 4 is tapered as shown toprovide a clearance space between shell 2 and tapered portion II. Thisclearance space is desirable to increase the dielectric surface betweeninsulator I0 and shell 2.

A center'wire or electrode I2 is mounted in a longitudinal opening orbore I4 of insulator 4. Electrode I2 is smaller than bore I4, leaving aclearance space. Because of the differences in the coeillcients ofexpansion of the insulator and available cements, it has been founddesirable to leave this clearance space free to avoid cracking of theinsulator. The upper portion of the 1ongitudinal bore through theinsulator is enlarged as indicate'dat I6. The juncture of the diilerentdiameter openings I4 and I6 forms a shoulder Il.

It is the object of this invention to provide a spark plug having theadvantages of the plug set forth above but without the tendency to chipping of the insulator. More speciilcally, it is the object of thisinvention to provide `means on the electrode near the sparking end butback from the insulator tip a short distance which will prevent contactbetween the electrode and the insulator tip during the said vibration.In fact, said means is intended to and does limit such vibration bymaterially decreasing the clearance between the insulator and theelectrode at a given point. The said means comprises a raised portion onthe electrode back a short distance from the insulator tip to preventcontact between the insulator tip and the electrode. This raised portionmay conveniently be made up of a plurality of closely spacedprojections, which may be formed by knurling.

Figure l shows a longitudinal sectional view of a complete spark plugmade according to this invention.

Figure 2 is a detail view of the sparking end of the insulator `andelectrode made according to this invention.

A collar 2li is provided on electrode I2. 'I'his collar cooperates withshoulder Il to position electrode I2 longitudinally in bore I4. A seal22 is bonded to insulator 4 and collar 2li to hold electrode I2 in placein opening I4 and to make a gas tight joint. The material of which seal22 is made is preferably a glass having a low coeilicient of expansionsuch as magnesium borate glass. This glass is 4preferably mixed with a1111er which serves as an electrical conductor. 'Ihe illler may begraphite, with or without metal inclusions or metallic compounds. A sealof Vthis type is described in Patent 2,106,578 to Karl Schwartzwalderand William Shuford Kirk, issued January 25, 1938.

Secured in the large diameter bore Ii is a suitable terminal 24.Terminal 24 is likewise held in place by the sealing material'22, someof which is shown as having passed upward along the lower end of screw24 to fill in the annular space between screw 24 and insulator 4.

Near the lower end of electrode I2 we have disposed a plurality ofcircumferential projections which are shown in Figures 1-4 as a verticalknurl 26. This knurl may be made by any suitable machining process, wellknown to those skilled in the art. The various projections provided onelectrode I2 by the knurl 26 provide a plurality of supports whereby theelectrode contacts the walls of opening I4 when laterally displaced.

Figure 4 illustrates another application of this invention. In this gureelectrode I2 is reduced in Figure 4 is the same as that illustrated inFigures 1-3.

Figure 5 illustrates an electrode having what is known as a horizontalknurl 2l in which the projections may comprise parallel concentric vrings on electrode I2.

The knurl is the preferred form of projection or support. This is truebecause, as is easily seen from the drawing, the knurl furnishes aplurality of contact points which engage the walls of opening Il in caseof vibration or other displacement of the electrode sidewise. Ii' theblow on the spark plug is severe enough, these contact points maydistort orA dei'orm somewhat. thus taking up the shock which in theabsence of/any projections might have to be taken up in impact betweenthe electrode and the insulator tip.

In Figure 6 electrode i2 has been pinched at spaced intervals to formraised portions Il which function in much the same manner to protect theinsulator as the above discussed knurl.

In Figure 7 the support comprises an annular ring of any suitable wire'32 disposed in an annular groove in electrode I2.

Figure 8 shows a raised portion comprising a plurality of fineprojections made by prickpunching electrode I2 to form an annular band34.

In Figure 9 electrode I2' has been stepped down at l2 to a smallerdiameter, as shown in Figure 4. Since the smaller diameter is on theelectrode at the insulator tip, displacement of electrode l2 sidewisewill result merely in contact of the shoulder 34 against the, side oi'opening I4.-

Figure 10 shows a heiically wrapped wire 36 forming annular supportsabout electrode l2 to eect contact above the insulator tip to preventchipping.

We claim: 1. In a spark plug7 an insulator, said insulator being taperednear the sparking end, a longitutudinal opening through the insulator,an electrode in the sparking end of said opening out of contact with thewalls thereof, a terminal in the other end of the opening, a pluralityof closely spaced. outwardly extending projections on the electrode nearits sparking end. and a bonded seal to form an electrical and mechanicaljoint between the electrode and the terminal and to hold the electrodein centered position in the opening.

2. In a spark plus, an insulator, said insulator being tapered near thesparking end, a longitudinal opening through, the insulator, said'opening having a relatively smaller diameter at the sparking end,ashoulder at the juncture of the two vdiameter openings. an electrode inthe smaller diameter part ci' the opening out of contact, with the wallsthereof, an enlargement on said electrode in engagement with saidshoulder. a plurality of closely spaced, outwardly extending projectionson the electrode near the sparking end, a terminal'in the largerdiameter part oi the opening, andan electrically conductive seal in theinner end of the larger diameter part of the opening to form anelectrical and mechanical Joint between the electrode and the terminal,said seal being bonded to both the electrode and the insulator.

3. The combination of claim 1, the sparking end of the electrode belowthe projections being of a smaller diameter than that portion of theelectrode above said' projections.

4. 'I'he combination of claim 2, the sparking end of the electrode belowthe projections being of a smaller diameter than that portion of theelectrode above said projections.

5. In a spark plug: an insulator having a lozgitudinal openingtherethrough and an electrode in said opening out of contact with theWalls of' the opening; said electrode having its sparking end projectingfrom one end of said opening and having a plurality of closely spaced,outwardly extending projections near its sparking end within the saidone end of the opening in the insulator.

6. A spark plug as in claim 5 in which the sparking end of the electrodebelow the projections is of a smaller diameter than that portion of theelectrode above the projections.

HECTOR RABEzzANA. ALEXANDER J. BA'ITEY. JOHN a; GRE'IjzrNGER.

